1. Field of the Invention
The present invention relates to methods of finishing a textile substrate. In particular, the invention relates to a digital procedure for producing a textile having encapsulated materials deposited thereon.
2. Description of the Related Art
The production of textiles traditionally takes place in a number of distinct processes. Roughly five stages can be distinguished in such production; the fibre production; spinning of the fibres; the manufacture of cloth (for instance woven or knitted fabrics, tufted material or felt and non-woven materials); the upgrading of the cloth; and the production or manufacture of end products. Textile upgrading covers a number of operations such as preparing, bleaching, optically whitening, colouring (dying and/or printing) and finishing. These operations generally have the purpose of giving the textile the appearance and physical and functional characteristics that are desired by the user.
During dying, the textile substrate is usually provided with a single full plane colour. Dying presently takes place by immersing the textile article in a dye bath, whereby the textile is saturated with an appropriate coloured chemical substance.
Coating of the textile is one of the more important techniques of finishing and may be used to impart various specific characteristics to the resulting product. It may be used for making the substrate fireproof or flameproof, water-repellent, oil repellent, non-creasing, shrink-proof, rot-proof, non-sliding, fold-retaining, antistatic etc. Coating of textile involves the application of e.g. a thin layer of an appropriate chemical substance to the surface of the textile substrate. The coating may serve to protect the textile substrate or other underlying layers. It may also be used as a basis or “primer” for subsequent layers or may be used to achieve desired special effects.
The usual techniques for applying a coating on solvent or water basis are the so-called “knife-over-roller”, the “dip” and the “reverse roller” screen coaters. A solution, suspension or dispersion of a polymer substance in water is usually applied to the cloth and excess coating is then scraped off with a doctor knife.
A further procedure sometimes employed for finishing of the textile is the use of immersion or bath techniques such as foularding. The textile is fully immersed in an aqueous solution containing the functional composition that is to be applied. Subsequent repeated cycles of drying, fixation and condensation are required to complete the operation. This leads to considerable use of resources, in particular water and energy. In general, the solutions, suspensions or dispersions used for such techniques have low concentrations of the desired functional composition
The conventional upgrading procedures require the performance of a number of sequential operations selected from impregnation (i.e. application or introduction of chemicals), reaction/fixing (i.e. binding chemicals to the substrate), washing (i.e. removing excess chemicals and auxiliary chemicals) and drying. Each of these sequential operations may need to be repeated a number of times e.g. repeated washing and rinsing cycles, which may entail a relatively high environmental impact, a long throughput time and relatively high production costs.
A significant characteristic of conventional upgrading techniques such as dying and coating is that they are performed over the complete surface of the article. This is often referred to as full font treatment. For certain treatments, there may be a desire to finish or coat only certain areas of the textile in order to provide particular characteristics to these areas. It is also often the case that treatments and chemicals used for finishing are particularly expensive and a limited but balanced distribution of the chemical may be sufficient. In such cases, the performance of the treatment over the full textile area may be inefficient and/or wasteful, especially if certain areas of the textile are to be discarded or have no need of the treatment.
Certain products that it would be desirable to include in a textile article are also sensitive to the environment. For this reason, their use has been limited in the past by difficulties in applying the product to the textile such that degradation does not occur. Other functional products have been suggested that it would be desirable to include on textile substrates. Nevertheless, adequate methods for depositing such products have hitherto been unavailable.
It has been suggested to incorporate drugs or medicaments within textile articles by attaching the drug to a carrier. A review of such carriers is to be found in an article by Breteler et al. in Autex Research Journal, Vol. 2 No 4 entitled Textile Slow Release Systems with Medical Applications, the contents of which are hereby incorporated by reference in their entirety. Carriers discussed include cyclodextrines, fullerenes, aza-crown ethers and also polylactic acid (PLA). No indication is given as to the precise manner in which these carriers could be applied.
The use of digital techniques for finishing textiles has been suggested in unpublished PCT application Nos. PCT/EP2004/010732 and PCT/EP2004/010731 both filed on 22 Sep. 2004 the contents of which are hereby incorporated by reference in their entirety.
It has been suggested in unexamined patent application No. JP61-152874 to Toray Industries, to impregnate a textile sheet with a functional composition in the form of dots. Various functional compositions are suggested including antibiotics, moisture absorbents, water repellents, antistatic agents, ultraviolet rays absorbents, infrared rays absorbents, optical whitening agents, swelling agents, solvents, saponifier, embrittlement agent, inorganic granules, metal granules, magnetic material, flame retardants, resistance, oxidants, reducing agents, perfumes, etc. The document indicates that traditional photogravure roll and screen print methods produce patterns of dots that may be too large, while in spraying techniques, the dot size and quantity of product deposited is difficult to control. The document proposes impregnating a textile with a functional composition in the form of dots, wherein a mean dot diameter is 30 to 500 microns and the occupied area ratio thereof is 3 to 95%. Although the document suggests the use of inkjet printing techniques, it identifies conventional inkjet devices as being unsuitable, in particular due to the high viscosity of traditional coating compositions. The document is concerned primarily with maintaining an identifiable droplet structure and preventing the droplets from running together. Furthermore, the document provides examples regarding the use of solutions but fails to address the problems of inkjet deposition of dispersions or suspensions.
Inkjet printers of various types are generally known for providing graphic images. Such printers may be desktop inkjet printers such as used in the office or home and are generally used for printing onto a particular type of paper substrate (printer paper), using small droplets (<20 pL) of water based inks containing colorants. Larger, industrial inkjet printers also exist for printing graphic images or date/batch codes onto products; these printers are typically printing onto non-porous substrates using solvent based inks containing colorants pigments. Such formulations are not however suitable for application to most textiles in particular due to lack of colour fastness. In order to print onto textiles using inkjet techniques, textile articles have in the past been pretreated with a coating onto which ink droplets may be applied. For upgrading purposes, most currently used coatings and finishing compositions are unsuitable for deposition using inkjet techniques. Industrial inkjet printers and nozzles that produce large droplets are generally designed for use with solvent based, coloured inks. Furthermore, the droplet volumes that can be jetted are extremely low, in the order of 50 pL and mostly insufficient for textile finishing, where a significant penetration into the fabric is necessary. Typical finishing formulations are mostly water based and generally have particle sizes that can cause clogging of the nozzles. Additional problems with foaming, spattering and encrustation have been encountered. When working with large numbers of nozzles operating continuously at up to 100 KHz, reliability and fault free operation are of prime importance. While indicating that conventional inkjet devices are unsuitable for applying finishing compositions, JP61-152874 fails to provide teaching regarding how this could be improved.